1. Field of the Invention
This invention relates to a semiconductor device inspection system for inspection of a semiconductor device, and more particularly to a system for inspecting the visual image of a semiconductor device by image pickup during manufacturing.
2. Description of the Prior Art
Conventionally, so-called wire bonding formed by connecting an IC chip and a lead on a base plate or substrate of a semiconductor device by means of a wire has been inspected manually and visually. Wire bonding items inspected included, for example, lack of a wire, breaking of a wire, mis-bonding of a wire (bonding of a wire to an incorrect position), the degree of wire projection, wire curling (unnecessary curling of a wire), raising of a bonding section, the position of bonding with respect to a pad or a lead, the dimensions and the shape of a ball or a stitch, and the like. Typically, the items from "lack of a wire" to "raising of a bonding section" are visually inspected by means of a microscope of low magnification having a wide visual field covering an IC chip and a bonding section formed around the chip.
The conventional inspection described above permits a three-dimensional configuration of a wire to be perceived by means of a binocular microscope; however, it has the disadvantage of requiring much time for inspection. Thus inspection efficiency is lowered because it is necessary to carry out the inspection on many items and on many bonding sections. Also, judgment of the correctness of the bonding is conventionally made on the basis of perception and/or the experience of an inspector, resulting in the inspection varying depending on the inspector. Further, visual inspection using a microscope is carried out in a direction from one side of a semiconductor device to the other side thereof. This leads to error in the inspection of deflection of a wire or the like because a distorted microscope image appears due to the distance from the microscope to the semiconductor device, resulting in deterioration of the accuracy of the inspection.
Recently, an image pickup device has been proposed which is adapted to use a lens of a high magnification to carry out plane image pickup substantially in parallel to a substrate for visual image inspection of a bonding section on a semiconductor device. However, in the image pickup device, it is necessary to adjust the focus of the device by varying the focal distance of the device or carrying out relative movement between the device and the substrate when a pad and a lead are not on the same image pickup plane.
Also, the conventional image pickup device unfortunately has a small focal depth because of using a lens of a high magnification, so that focus adjustment of the device is highly troublesome.
Further, an attempt has been made to use the image pickup device for inspecting the amount of deformation of a wire in the direction of its height. For this purpose, a camera of the device was vertically moved to focus the camera on each vertical position of the wire. However, it is required to horizontally move the camera with respect to each pad and lead because the lens has a high magnification and a small visual field, resulting in substantial deterioration of inspection efficiency.
Further, it takes much time to transfer the image pickup device for image pickup, resulting in a lowering in inspection efficiency and speed
Accordingly, it would be highly desirable to develop a system for inspection of a semiconductor device which is capable of determining the correctness of the inspection, objectively accomplishing the inspection and minimizing or substantially eliminating errors in the inspection, and minimizing errors in the inspection due to a distorted image which appears due to distance, to thereby inspect the visual image of a semiconductor device with high accuracy and efficiency and at high speed.